A fire spell might be consulted to learn whether a strange material is flammable. An ice spell might be consulted to learn how much longer winter will last. A bewitch spell might give advice about improving social status with the local elite. A knock spell might explain something about the workings of a door rather than merely opening it.
This consultation is not a simple siphoning of information from an ancient text the spellcaster has memorized. The spell manifests as an incorporeal, transparent personality visible only to the caster, who appears to be speaking to himself, in his own voice and in another, strange voice that he thinks fits the personality of the spell. He is not doing this for comfort, fun, or drama; it's a necessary result of the consultation. To avoid appearing even more insane and eccentric than casters usually appear, many prefer to find somewhere private when consulting a spell. Time constraints often prevent this, of course.
The spells translate their thoughts into words, but they don't translate the spell's manner of thought. Their perspectives might sometimes be a bit cryptic, overcomplicated, or simplistic.
When commanding a knock spell, a caster who asks, "Tell me about this door," might be told, "This portal wants greasy disease to flow." This might be a warning about a poisonous doorknob or it might be a hint about applying oil to the keyhole. Hopefully, the caster will continue the conversation if the answer is not clear.
(I probably stole this idea from somewhere, somehow. I have no idea. I've been reading everything OSR, all the time.)
Mechanics
Instead of allowing a spell to have its usual effect, a spellcaster may expend the spell to speak aloud to a manifestation of the spell. The spell is an expert on relevant information. Only the caster will be able to see or hear the manifestation. Those nearby will hear the words the spell is speaking coming from the caster's lips, as if he is speaking nonsense to himself.
If you use a standard OSR D&D sort of thing, this effect increases with spellcaster level. [Level]x10 = # of minutes the conversation may last.
If you use GLOG, use: [sum]x10 = # of minutes the conversation may last.